PARIS -- Mexico's foreign secretary said Monday the country may take a dispute over U.S. plans to build a fence on the Mexican border to the United Nations.

Luis Ernesto Derbez told reporters in Paris, his first stop on a European tour, that a legal investigation was under way to determine whether Mexico has a case.

The Mexican government last week sent a diplomatic note to Washington criticizing the plan for 700 miles of new fencing along the border. President-elect Felipe Calderon also denounced the plan, but said it was a bilateral issue that should not be put before the international community.

Derbez said Monday after meeting with French Foreign Minister Philippe Douste-Blazy that it was a "shame" U.S. immigration policy had been used for what he claimed was a short-term political gain in the lead-up to midterm elections in the U.S. in November.

He said he discussed the issue with Douste-Blazy, and planned to bring it up in meetings with his Spanish and Italian counterparts during visits to Madrid and Rome. He vowed to work on the case until the "very last day" of President Vicente Fox's term, which ends Dec. 1.

The U.S. Senate approved the border fence bill last month and President Bush has said he will sign it into law _ despite last-minute pleas from the Mexican government for a veto.

"What should be constructed is a bridge in relations between the two countries," Derbez said.